1. Field of the Invention
This invention relates to a printer, more particularly, to a printer including a means for detecting a thickness of a printing media, such as printing sheets or papers, hereinafter referred to as "printing sheet".
2. Description of the Related Art
Recently, various developments have been made in printers to increase the range of use thereof, e.g., the capability to process printing sheets not having a constant thickness. For example, in some printers, several sheets of the same thickness can be set at one time together with various kinds of single sheets having different thicknesses, such as postcards or tracing paper. Nevertheless, although printing sheets having various thicknesses can be used in a printer, the thickness of a printing sheet is a very important factor when determining a gap between a print head and printing sheet, and thus the sheet thickness sometimes may affect the printing impact and reduce the quality of the printed product.
Conventionally, a gap between a print head and a printing sheet is manually adjusted by a lever. However, during such an adjustment, sometimes the ink ribbon is loosened or the printing sheet is stained by undue contact with the ink ribbon. Also, the operator may sometimes set the gap incorrectly.
Japanese Unexamined Patent Publication (J-A) Nos. 60-250977 and 60-234872 (U.S. Pat. No. 4,676,675) disclose a printer having a thickness compensation device comprising a position sensor mounted on a carriage for detecting the printing sheet. The position sensor in these prior arts is constructed by a piezo-electric rubber element and directly mounted on the carriage, so that a precise position of the printing sheet is not always detected due to a resistance of the rubber element, which has only a small area in contact with the printing sheet.
JP-A Nos. 56-142087, 57-152976 and 58-3893 disclose a printer in which a carriage having a print head mounted thereon is in contact with a platen via a printing sheet at a constant pressure, so that a constant gap can be maintained between the print head and printing sheet. However, the printer disclosed in these prior arts is not provided with a thickness detection switch.
JP-A Nos. 57-163588, and 57-152975 disclose a printer in which the thickness of a printing sheet is detected by a potentiometer, and a gap between the print head and the printing sheet is controlled on the basis of data detected by the potentiometer. However, these prior arts do not disclose a thickness detection means mounted on the carriage.
JP-A Nos. 62-55179, 58-72491 and 61-171377 disclose a printer used in the same field of the art, but this printer does not have a printing sheet thickness detection switch or sensor.